It has long been known that cardiovascular problems are caused by the presence of atherosclerotic plaque on the walls of veins and arteries, especially coronary arteries. For some time, there has been interest in the use of laser energy to remove plaque and to treat abnormalities on internal organs in the body. Typically, it is proposed to use a catheter that contains optical fibers for transmitting the laser energy through the catheter to the area that is to undergo treatment. Lasers have also been used to treat other medical problems such as tumors or other abnormalities in the colon, esophagus, prostrate and other areas of the body.
U.S. Pat. No. 4,576,177 to Webster discloses a catheter which includes optical fibers in combination with an ultrasonic transducer having the capability of transmitting and receiving ultrasonic signals. The reflections of the ultrasonic signals from the tissue are received by the transducer to provide information as to the character and configuration of the tissues so that the laser energy can be applied properly to the plaque lesion and not to unoccluded artery walls or other healthy tissues.
In the device disclosed in the Webster patent, the ultrasonic transducer takes the form of a flat ring which is oriented at an angle to the axis of the catheter. With this arrangement, it is necessary to rotate the catheter through a full 360.degree. circle in order to direct the ultrasound at the entire circumference of the artery. The need to manually rotate the catheter is at best a severe inconvenience and an inaccurate procedure because the catheter cannot be accurately stepped through incremental arcs in order to provide a reliable profile of the arterial plaque. If the ultrasound techniques are inadequate to provide the instrument with an accurate configuration of the plaque, the laser energy can be misdirected such that it is not only ineffective in treating the problem but also possibly destructive of healthy tissues.